Technical Field. This invention relates to measuring devices, and more particularly to a gauge for checking the diameter of the bore of a shotgun barrel.
Background: Shotguns come in a variety of sizes, the size being determined by the bore of the barrel. Commonly available shotgun sizes include the 10 gauge, the 12 gauge, the 16 gauge, the 20 gauge, the 28 gauge and a 410. Historically, each of these gauges corresponded to the barrel diameter determined by the diameter of a ball of lead weighing a predetermined amount. In the case of a 10-gauge, the barrel diameter or bore corresponded to a ball of lead weighing one-tenth of a pound. Similarly, the barrel diameter of a 12-gauge corresponded to the diameter of a ball of lead weighing one-twelfth of a pound, and so on. The barrel diameter of a .410 shotgun corresponded to the barrel diameter determined by the diameter of a ball of lead weighing one fortieth of a pound.
Over time, a variety of modifications have been standardized, as can be seen in Table 1.
TABLE 1 ______________________________________ TABLE OF SHOTGUN BORE CONSTRICTIONS GAUGE 10 12 16 20 28 410 NEW AMERICAN STANDARD ______________________________________ NOMINAL BORE 0.779 0.729 0.667 0.617 0.550 0.410 DIAMETER CYLINDER 0.000 0.000 0.000 0.000 0.000 0.000 SKEET I 0.005 0.005 0.004 0.004 0.003 0.002 IMPROVED CYLINDER 0.010 0.009 0.007 0.006 0.005 0.004 SKEET II 0.015 0.012 0.010 0.009 0.007 0.006 MODIFIED 0.020 0.019 0.015 0.014 0.012 0.008 IMPROVED MODIFIED 0.025 0.025 0.020 0.019 0.016 0.011 FULL CHOKE 0.035 0.035 0.028 0.025 0.022 0.015 EXTRA FULL 0.040 0.040 0.035 0.027 0.024 0.021 ______________________________________
Gunsmiths are frequently asked to make modifications to existing barrels for a variety of reasons including age of the gun and enhancement of performance. As a result, a wide variety of actual barrel sizes may be identified by any of the several common nominal bore diameters.
A similar variety of sizings as those shown above at Table 1 are also recognized by the Old American Standard and the New European Standard, although the variation for any given choke for these other recognized standards will vary from those recognized by the New American Standard. See Table 2 and Table 3.
TABLE 2 ______________________________________ TABLE OF SHOTGUN BORE CONSTRICTIONS GAUGE 10 12 16 20 28 410 OLD AMERICAN STANDARD ______________________________________ NOMINAL BORE 0.775 0.725 0.662 0.615 0.550 0.410 DIAMETER CYLINDER 0.000 0.000 0.000 0.000 0.000 0.000 SKEET I 0.004 0.003 0.003 0.002 0.002 0.001 IMPROVED CYLINDER 0.007 0.006 0.005 0.004 0.003 0.002 SKEET II 0.012 0.011 0.009 0.007 0.006 0.004 MODIFIED 0.016 0.015 0.012 0.010 0.008 0.005 IMPROVED MODIFIED 0.025 0.023 0.018 0.016 0.013 0.010 FULL CHOKE 0.035 0.030 0.024 0.021 0.017 0.014 EXTRA FULL 0.040 0.035 0.032 0.025 0.023 0.020 ______________________________________
TABLE 3 ______________________________________ TABLE OF SHOTGUN BORE CONSTRICTIONS GAUGE 10 12 16 20 28 410 NEW EUROPEAN STANDARD ______________________________________ NOMINAL BORE 0.780 0.730 0.673 0.619 0.544 0.415 DIAMETER CYLINDER 0.000 0.000 0.000 0.000 0.000 0.000 SKEET I 0.005 0.005 0.004 0.003 0.004 0.005 IMPROVED CYLINDER 0.010 0.010 0.008 0.006 0.008 0.010 SKEET II 0.015 0.015 0.012 0.011 0.012 0.016 MODIFIED 0.020 0.020 0.017 0.015 0.016 0.022 IMPROVED MODIFIED 0.025 0.025 0.025 0.022 0.022 0.028 FULL CHOKE 0.035 0.035 0.033 0.029 0.028 0.034 EXTRA FULL 0.040 0.040 0.040 0.031 0.032 0.035 ______________________________________
What is needed is a simple gauge which would allow dealers and collectors of used arms to easily identify the size of the bore of any given shotgun. The object, then, of the present invention is to provide such a gauge.
This objective is met by a flat gauge having a tapered width, the gauge having inscribed or etched on one face markings which would allow the user to identify the bore of a given shotgun. These gauges would be made available in any of the recognized standards including the New American Standard, the Old American Standard and the New European Standard.
Another objective of the present invention would be to provide a gauge which is simple and inexpensive to manufacture.